After attending Data Center World I came away feeling that practically everyone worked for a corporate data center that was run by the company. There was a Target presentation about a finely tuned center with awesome policies and procedures. There was a presentation about how the state of Oregon consolidated all of their data centers into one. I do however, also see a fair number of companies that stick to the "do what we do best and outsource the rest" mentality.
Two examples I ran across recently of keeping things in house, were Workstream opening a new data center and liquid web hosting opening a second data center.
Looking through some of my old bookmarks I found this article that gives a lot of good statistics about outsourcing. I am still a strong believer in outsourcing what your company does not excel in. Many take it to the extreme of outsourcing everything that is not the core business of the company. As with most things I suppose it is just a mix of working with what you have, beliefs of management of the company and timing. I have worked with another company recently that did outsource a number of things and for whatever reasons they hired a new CIO and had him start bringing everything back in house.
I think in the end it is just a numbers game and proving to the board of directors what you believe works best and ROI.